Which manifestation is characteristic of hypomagnesemia?

Hypomagnesemia, or low magnesium levels in the blood, is associated with several clinical manifestations, among which cardiac arrhythmias are particularly significant. Magnesium plays a critical role in maintaining normal cellular function, including the electrical activity of the heart. When magnesium levels drop, it can lead to disturbances in cardiac conduction and result in arrhythmias, which are irregular heart rhythms that can be life-threatening if not addressed.

Arrhythmias associated with hypomagnesemia can manifest as various patterns on an electrocardiogram (ECG), such as prolonged QT interval, T-wave changes, and potentially more serious complications, including torsades de pointes. Hence, cardiac arrhythmias are a hallmark feature of hypomagnesemia that healthcare providers monitor closely in affected individuals.

The other options do not appropriately reflect the manifestations of hypomagnesemia. Muscle relaxation is generally associated with high magnesium levels, while low energy is a symptom that may arise due to various metabolic issues rather than high energy. A normal heart rate would not typically be observed in the presence of hypomagnesemia, as the condition often leads to increased cardiac irritability and irregularity in heart rhythms.